Reading and Writing Items Using Expressions
In DynamoDB, you use expressions to denote the attributes that you want to read from an item. You also use expressions when writing an item, to indicate any conditions that must be met (also known as a conditional update) and to indicate how the attributes are to be updated. Some update examples are replacing the attribute with a new value, or adding new data to a list or a map. This section describes the different kinds of expressions that are available.
For backward compatibility, DynamoDB also supports conditional parameters that do not use expressions. For more information, see Legacy Conditional Parameters.
New applications should use expressions rather than the legacy parameters.